A significant years-long investigation into pharma company price hikes may come to a head by the end of 2016. The Justice Department is reportedly mulling antitrust charges against more than a dozen major generic drug makers for alleged price fixing, according to Bloomberg.

The companies being investigated include Mylan (MYL) (now infamous for its price hike on the EpiPen); a subsidiary of Endo (ENDP); Teva (TEVA); Lannett; Sun Pharma; Impax Laboratories; and others. These drug makers produce a major share of the world’s generic medications.

The Justice Department declined to comment on the matter to Fortune. But many of the firms have previously disclosed receiving subpoenas related to the investigation.

In late 2014, the Justice Department issued two subpoenas to Lannett and Impax in order to question them about potential communications they’d had with rival drug companies amid a period of soaring medicine prices.

That news came just one month after Rep. Elijah Cummings, the ranking Democrat on the House Government and Oversight Committee, and Sen. Bernie Sanders of Vermont said they’d be looking into generic drug price hikes. The relevant companies have said that they will fully comply with the investigation.

Still, Bloomberg’s report sent the various firms’ stock prices tumbling on Thursday in the middle of a trading session that had already been brutal for health care companies. Mylan, for instance, tumbled 7% while Lannett, Impax, and Endo were all down about 20% or more at one point.